Silicon-steel.



W. E. RUDER.

SILICON STEEL.

APPLIGATION FILED JUNE 22, 1912.

1,110,010. Patented Sept. 8, 1914.

I II I lllllllll WITNESEIEE: INVENTEIRI W DY wiLLiAMfieRuDER.

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/ Hi5 ATTEIRNEY UNITED STATES ,PATENT OFFICE.

WILLIAM E. RUDER, 0F SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SILICON-STEEL.

Specification of Letters Patent.

Patented Sept. 8,1914.

Application filed June 22,1912. Serial No. 705,251.

To all whom it may concern:

Be it known that I, WILLIAM E. RUDER, a citizen of the United States, residing at Schenectady, in the countyof Schenectady, State of New York, have invented certain new and useful Improvements in Silicon- Steel, of which the following is a specification.

My invention has reference to the conversion of ordinary silicon steel, particularly in sheet form, to a new state in which this material exhibits lower hysteresis than any other magnetic material heretofore made and known to me.

By the term silicon steel, I wish to include, in addition to the alloys of iron with a suitable percentage of silicon, the alloys of iron with other materials which have the same or like characteristics. Such alloys, and particularly the alloy of iron with from three to five per cent. of silicon, have heretofore been manufactured in sheet form by well known processes for use as cores for transformers and other alternating current apparatus. The sheets have afterward been annealed by heating them to temperatures anywhere between 7 00 C. to 1000 C. and were then allowed to cool slowly. The product resulting from these old processes has a hysteresis loss considerably lower than that of carbon steel or iron in its purest commercial form.

My invention is directed to a new process of annealing silicon steel, and particularly silicon steel sheets, which results in the production of a new material in which the hysteresis loss is remarkably low. The new product constitutes another part of my invention.

Broadly speaking, my new process of an nealing silicon steel consists in subjecting this material to a high temperature and to such other conditions which conspire with the high temperature to remove the impurities, such as sulfur, phosphorus and carbon, but particularly the oxygen combined with or occluded in the silicon steel, so that all oxidulated compounds in the steel become reduced and the new material is practically non-oxygenous.

The structure of ordinary silicon steel is an aggregation of grains that are so small that when the surface of a sheet of that material is etched by an acid, the same presents to the unaided eye the aspect of evenly .dis

' same as the old material tributed fine granules which'the unaided eye cannot resolve but which under the microscope appear distinctly separated. On the other hand, the surface of this same material, after it has been converted by my improved annealing process, appears to the un aided eye as a mass of distinct granules the appeared under the microscope. Etching intensifies this appearance. In other words, the minute, practically invisible grains of the ordina silicon steel have coalesced into a smaller number of much larger grains that are plainly visible to the unaided eye. Under a high powered microscope, the grains in each case are revealed as aggregations of minute crystals.

my opinion, the reduced hysteresis loss of the material produced by my process is due mainly to the elimination from the same of the combined or occluded oxygen, and, in a lesser degree, to the conversion of the minute, practically invisible grains, or aggregations of crystals, into larger, plainly visible grains. I

In the accompanying drawings, Figure 1 shows a vertical section of one form of the annealing furnace which may be used in the practice of my process; Fig. 2 is a plan view of the same with the top removed; Fig. 3 is a diagrammatic view of an annealing furnace supplied with reducing gas; and Fig. 4 illustrates the appearance of the steel before and after the annealing process. The particular furnace shown in the drawing is only one of many forms that may be used, v

and my invention is not limited to the use of this particular or any particular form of furnace.

Referring to the drawings and now especially to Figs. 1 and 2, it will be seen that the furnace proper is situated withina tank 1 containing water which surrounds and cools the furnace proper. envelop of the furnacevconsists of a box 2 made of iron, or gun metal provided with a coating of tin. Access to the heating zone may be had by removing the cover 3, which may be bolted to the box 2. Lead gaskets 4 may be used under the cover to make the joint tight. The heating elements of the furnace consistof four graphite grids, two of which, 5 and 6, are shown in Fig. 1, the other two as indicated in' Fig. 2 beingsituated back of the grids 5. ands: :Itjaof The main are till

still mod course, not necessary that the grids shall have the zigzag lol rn here indicated, this being merely usedin soine cases to secure greater resistance for a given length, Gurrent is supplied to these resistance elements by way of conductors attached to watercooled copper tubes Z and 7', which are in turn clamped to copper blocks 8 and 8, which latter make direct-contact with the grids, For example, as indicatedin Fig. l, the current path is from conductor 9 to grid 5 and :lrorn thence through a graphite block 10 to grid 6. The cross connection ll makes contact with the lower grid upon the other side of the furnace, the current returning through the upper grid to con doctor 1%. The copper terminals 8 and 8 chilled by a cooling lluicl conveyed, as indicated, by the tubes 13 and let. The lorrner is connected to the copper tube '3' attached to heating element 5 and the latter to the tube 7 connected to the terminal back of the one shown, whereby the cooling lluid escapes. In the furnace illustrated, the heating zone is surrounded by a, heat insulating screen 15 consisting oil graphite bones containing a packing of graphite powder,

or the screen may be formed of hrebriclr.

When it is desired to anneal a charge oil silicon steel sheets, the charge is assembled in packs and is placed between the graphite heaters, the (201131 is securely bolted and the turnace evacuated through pipe it The temperature of the furnace is then raised by the passage of current through the heating grids to or above 1200 C. and as high as practicable without endangering the integrity oi the sheets; and l have found that this temperature may safely be carried up to l32h U. ln accordance with nay inven tion, this high temperature is preferable and isrnaintained for a period ot time depending upon the amount of material; for a charge ct about 500 pounds, a run ot about the hours is sufficient, but when annealing say 100 pounds or less, only about two hours is required.

During all this time, the eirhaust is operating through. the pipe 16, whereby the requisite low pressure within the :lnrnace is maintained. This pressure usually should be as low as about 2 to 2.5 millimeters of mercury, or even lower. The residual gas is probably largely nitrogen and carbon nionoin'd formed by interaction of oxygen with the heated grids. llnder these pressures and temperatures, all or practically all the carbon, sulfur, phosphorus and particularly the oxygen are removed, and the gases thus evolved are continuously euhausted. litter the current is turned ed, the material is allowed to cool within the furnace to a pointwhere its removal and consequent exposure to the air will not cause any up preeiable oxidation.

While all pressures between 2 and 2.5 mil liineters of mercury and all temperatures be tween 1100" (J. and 1325 C. give good re sults, it is preferable to maintain the lowest pressure (:2 millimeters) and the highest temperature (l325 G), but all variations Within the limits above indicated are permissible.

A more direct reduction of the oxids contained in the silicon steel is obtained Without a partial vacuum, by the introduction of a reducing gas within the furnace while the material is being annealed. This is indicated in ig. 3, where a pipe 17 is shown as tapped into the upper partof the furnace and through which hydrogen is passed into and through the turnace and out by the pipe 18, where it may be allowed to burn, as in dicated. The result obtained by the use of either of these two furnaces is the same. The chemical change in the material is a removal of all or practically all the oxygen contained in the material or in any oi the oxide which ima'i-itably occur in the same. The magnetic change is a remarkable reduction of hysteresis losses and the physical change is a coalescence of the small grains into very much larger ones, so that they become clearly apparent to the unaided eye after etching. '5 his latter change is shown n Fig. l, in which 1:) illustrates the aspect to the unaided eye, but after etching, of the material before it has been improi'ed in accordance withniy invent-ion, while at 20 is illustrated the appearance of the improved material. Usually the granular structure is visible without etching but it is emphasized by etchin its hereinbetore stated, I ascribe the re duction of hysteresis losses in my improved product mainly to the reduction of the oxide which it normally contains and also in part to the tact that the normal grains of silicon steel are coalesced into a lesser number of much larger grains.

l have found that this coalescence of the normal. small grains into larger grains can also be obtained when the silicon steel is heated in any ordinarymanner to a sufii ciently high temperature Within the range of 1100 and l3'25 C, but that While this in itself produces a slight reduction of the hysteresis losses, the gain in this respect is slight only becomes marked when the oxids contained in the material are reduced in accordance with my invention. Consequently, it may divide my process into two steps; nainely, first producing the aggregation oi the normal small grains 0t silicon steel into larger ones by heating the material above 1100 C. in any ordinary manner, and particularly in the ordinary manner with the free admission of air, and subsequently reducing the oxide in the material i heroiubetoro indicated. it the process is ill) thus divided into two steps, the temperature in the vacuum or hydrogen furnace need not be raised as high as when the process is carried out in one operation; and I have found that by the two-step process the temperature in the reducing furnace may be as ow'as 1000 C. and still give highly improved results. In fact, in some cases it may e desirable to anneal the iron in hydrogen at a temperature range as low as 790 to 900 C. without a previous firing treatment at higher temperature. In this case an improvement of about 10 per cent. in hysteresis action is obtained over the corresponding air anneal.

When, in the ractice of my invention, the

lower pressure 2 millimeters) coupled with' the highest temperature 1325 C.) is employed, I have found that the hysteresis watt loss per pound of steel per cycle, at a magnetic density B=10,000, may be as low as 0.0060, which is more than 30 per cent. below the hysteresis watt loss of the best material heretofore made and known to me.

Whatl claim as new and desire to secure by Letters Patent of the United States is:-

1. The process of reducing the hysteresis of silicon steel, which consists in removing the impurities fromthe steel at a high temperature.

2. The process of reducing the hysteresis action of silicon steel, whlch consists in removing the oxygen from the steel at a high temperature.

3. The process of reducing the hysteresis action of silicon steel, which consists in causing a coalescence of the normal small grains of this material into larger grains and removing the oxygen from the same.

4. The process of reducingthe hysteresis action of silicon steel, wh1ch consists in subjecting the same to oxygen removing conditions at a high temperature.

5. The process of annealing silicon steel, which consists in subjecting the material to a high temperature under a gas pressure at or below the dissociation pressures of the oxids in the said material for the prevailing temperature.

6. The process of annealing silicon steel, which consists in heating the same to or above 1100 C. in a partial vacuum.

7. The process of annealing silicon steel, which consists in heating the same to a temperature of 1100 C. to 1325 C. under a maintained gas pressure of about 2 to 2.5 millimeters of mercury.

8. The process of annealing silicon steel, which consists in heating the same in a vacuum furnace for several hours to a temperature of 1100 C. to 1325 C.

9. The process of annealingsilicon steel which consists in subjecting the material to oxygen removing conditions at a temperature at least as igh as '(90 C.

10. As a new article of manufacture, nonoxygenous silicon steel, giving low hysteresis losses in electrical a paratus.

11. As a new article 0 manufacture, nonoxygenous silicon steel exhibiting to the unaided vision a surface structure of large separable granules.

In witness whereof, I have hereunto set my hand this 21st day of June 1912.

WILLIAM E. RUDER.

Witnesses:

BENJAMIN B. HULL,

HELEN Onrom). 

